This invention relates to multi-speed power transmissions and, more particularly, to multi-speed planetary type power transmissions providing six and seven forward speed ratios.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive mechanism. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times as the transmission ratios are interchanged. The number of forward speed ratios that are available in a transmission determines the number of ratio interchanges that can occur and therefore the number of times the engine torque range can be repeated.
Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 6,083,135 issued to Baldwin et al. on Jul. 4, 2000; and European Patent Application No. EP 1 033 510 A1 published Jun. 9, 2000.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ six-speed transmissions, such as Polak, passenger cars are still manufactured, for the main part, with three and four speed automatic transmissions, and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gearsets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio. The Lepelletier and the EP publications each employ three planetary gearsets, three clutches and two brakes to provide six forward speed ratios and one reverse ratio. One of the planetary gearsets in each of these publications is positioned and operated to establish two fixed speed input members for the remaining two planetary gearsets.
It is an object of the present invention to provide an improved multi-speed planetary transmission.
In one aspect of the present invention, an input gearset and a multi-speed Ravigneaux gearset are combined to provide at least six forward speed ratios.
In another aspect of the present invention, the input gearset provides a reduced speed input to the Ravigneaux planetary gearset during at least two of the forward drive ratios and one reverse drive ratio.
In yet another aspect of the present invention, the input gearset has a fixed planet carrier member, which is secured to a transmission housing.
In still another aspect of the present invention, a housing or center support is secured to the fixed planet carrier member of the input gearset.
In yet still another aspect of the present invention, the center support slidably supports piston members for three rotary type torque-transmitting mechanisms.
In a further aspect of the present invention, the center support also provides an outer race for a one-way torque-transmitting mechanism.
In a still further aspect of the present invention, the Ravigneaux planetary gearset includes two interconnected ring gear members, which are also interconnected continuously with a transmission output shaft.
In a yet further aspect of the present invention, the input gearset has a sun gear member, which is continuously driven by a transmission input.
In a still further aspect of the present invention, the power transmission incorporates five friction type torque-transmitting mechanisms and one one-way type torque-transmitting mechanism, which are active in combinations of two to provide at least six forward speed ratios between a transmission input shaft and a transmission output shaft.
In a yet still further aspect of the present invention, the torque-transmitting mechanisms are also effective in combinations of two to establish seven forward speed ratios and one reverse speed ratio between the transmission input shaft and the transmission output shaft.